The use of disposable test elements has become commonplace to measure the presence and/or concentrations of selected analytes in test samples. For example, patients suffering from diabetes and similar medical conditions often engage in self-monitoring of blood glucose wherein the patient monitors his or her blood glucose levels. The purpose of monitoring the blood glucose level is to determine the concentration level and then to take corrective action, based upon whether the level is too high or too low, to bring the level back within a normal range. The failure to take corrective action can have serious medical implications. Glucose monitoring is a fact of everyday life for diabetic individuals. Failure to test blood glucose levels properly and on a regular basis can result in serious diabetes-related complications, including cardiovascular disease, kidney disease, nerve damage and blindness.
A number of analyte measurement systems are currently available that, in combination with a disposable test element, permit an individual to test or measure for a targeted analyte in a test sample. For example, a disposable test element can be used with a glucose meter to measure the amount of glucose in a blood sample electrochemically or optically. In current glucose meters, the information displayed as a consequence of a successful blood glucose measurement is the respective blood glucose value, typically shown in mg/dL or mmol units, and perhaps the time and date the measurement was performed. This information in combination with calculation of planned or known intake of carbohydrates or planned or known activities and knowledge of other situational or individual factors is in most cases sufficient to allow diabetics to adjust or derive their dietary intake and/or an immediate dose of insulin to inject to control blood glucose level on the short-term. Also, in case of low glucose values, diabetics can detect the need for intake of sugar to avoid hypoglycemia.
Current trends in analyte testing and test elements require smaller test samples and faster analysis times. In the case of diabetics for example, this provides a significant benefit to the patient, allowing the use of smaller blood samples that can be obtained from less sensitive areas of the body. Additionally, faster test times and more accurate results enable patients to better control their blood sugar level.
In one form, disposable test elements used with meters for electrochemically measuring the amount of glucose in the blood sample include an electrode arrangement and a coating of a reagent material for producing an electrochemical signal in the presence of glucose. Numerous variations of the reagent coating are possible depending upon the specific analyte(s) to be tested, and there are typically numerous chemistries available for use with each of the various analytes. Generally speaking, however, it is desirable to form the reagent layer in the test strip or biosensor as thin and as uniform as possible. For example, a thinner reagent layer will hydrate more quickly and will therefore produce a quicker test result. In addition, variations in thickness of the reagent layer increasingly affect the accuracy of the test result. As a result, non-uniformities in the reagent layer can lead to inconsistency in filling a sample receiving chamber of the test element, prolonged dissolution intervals, and inconsistent mixing of the reagent with the sample fluid, and, ultimately, poor test results.
Nonetheless, while forming a thin and uniform reagent layer that hydrates quickly with a small volume is desirable, it is not easily obtained because of the difficulties in working with small volumes of liquid reagent, variations in the substrate material of the test elements, and limitations in processing equipment. For example, when the reagent layer is applied to a test element by a slot die coating process, current attempts at achieving thickness uniformity of the reagent layer on the substrate of the test element are made by moving the slot die relative to the substrate in order to adjust the thickness of the reagent layer in response to, for example, thickness variations of the substrate. However, the ability to control thickness uniformity of the reagent layer by this approach is limited because movement of the slot die relative to the substrate can often be delayed and/or result in a reduced coating gap between the discharge end of the slot die and the substrate, which can result in wet film deformities, such as streaking, caused by debris trapped between the slot die and the substrate and/or otherwise impact the coating process due to variations in the thickness of the substrate.
With regard to a slot die coating process, certain other methods and parameters relating to the reagent coating layer itself are also known to facilitate thickness uniformity. See, e.g., U.S. Pat. No. 7,749,437 and U.S. Pat. No. 7,879,619, the disclosures of which are hereby incorporated herein by reference in their entireties.
In view of the foregoing, and given the ramifications of accurately analyzing selected analytes in test samples, there remains a need for improvements in the application of the reagent layer on test elements.